Solar cells are typically photovoltaic devices that convert sunlight directly into electricity. Solar cells typically include a semiconductor (e.g., silicon) wafer (substrate) that absorbs light irradiation (e.g., sunlight) in a way that creates free electrons, which in turn are caused to flow in the presence of a built-in field to create direct current (DC) power. The DC power generated by several solar cells may be collected on a grid placed on the cell. Solar cells are typically made using square or quasi-square silicon wafers that are doped to include one or more n-type doped regions, and one or more p-type doped regions. Such solar cells (also known as silicon wafer-based solar cells) are currently the dominant technology in the commercial production of solar cells, and are the main focus of the present invention.
A desirable solar cell geometry, commonly referred to as the interdigitated back contact (IBC) cell, consists of a semiconductor wafer, such as silicon, and alternating lines (interdigitated stripes) of p-type and n-type doping. This cell architecture has the advantage that all of the electrical contacts to the p and n regions can be made to one side of the wafer. When the wafers are connected together into a module, the wiring is all done from one side. Device structure and fabrication means for this device have been described previously in co-owned and U.S. patent application Ser. No. 11/336,714 entitled “Solar Cell Production Using Non-Contact Patterning and Direct-Write Metallization”, which is incorporated herein by reference in its entirety. On May 12, 2008, SunPower Corp. (San Jose, Calif., USA) announced achieving 23.4% efficiency in a prototype IBC cell (see http://investors.sunpowercorp.com/releasedetail.cfm?ReleaseID=309613).
A problem with IBC solar cells is that the conventional fabrication process used to produce IBC cells is quite complicated and, hence, more expensive as compared to the fabrication processes require to produce conventional ‘H-pattern’ solar cells. According to D. H. Neuhaus and A. Munzer, “Industrial Silicon Wafer Solar Cells” (Advances in Optoelectronics, vol. 2007, pp. 1-15, 2007), IBC cells require seventeen process steps (minimum) in order to complete the cell fabrication process, whereas conventional H-pattern solar cells require only nine steps.
What is needed is a method for producing IBC-type solar cells that overcomes the deficiencies of conventional production methods by reducing the manufacturing costs and complexity, whereby IBC-type solar cells can be produced at substantially the same or lower cost as conventional H-pattern solar cells.